As described in the French patents FR 2 699 121, FR 2 713 557 and FR 2 713 558, such a rim has, seen in meridian section, a first seat whose axially outer end is on a circle with a diameter less than the diameter of the circle on which the axially inner end is situated (such a seat is said to be inclined outwards), a relatively wide rim bearing surface intended to receive a removable tread support ring, possibly a mounting well, and a second rim seat, a either identical to or different from the first rim seat. The rim, a tire having an adapted meridian carcass reinforcement profile and bead shape, and a removable support together form a rolling assembly which is of high performance in the case of running at low pressure or even zero pressure.
The patent FR 2 720 977 describes a method of mounting, on a single-piece rim, a tire comprising a first bead and a second bead which will be mounted respectively on the first and second rim seat, and a removable support. The mounting method is such that:    the support is, in a first step, placed inside the tire;    the second bead and the support are placed on the rim, from the side opposite to the second rim seat, until they are positioned on the rim bearing surface,    the process of fitting the support on the rim bearing surface is completed and the first bead is mounted on the first rim seat; and    the second rim is mounted on the second rim seat.
The document EP 1 048 496 A1 describes a device for implementing this mounting method in which the first rim and the support are simultaneously fitted on the rim by progressive application of an axial force against the first bead of the tire, itself being seated against the adjacent wall of the support. The tool applying the axial force is a freely rotating roller whereby this fitting takes place during a rotation of the rim which also drives the tire and support in rotation. This method is effective in the case of supports which, in the state in which they are fitted on the rim bearing surface, are in contact with the first tire bead or very close to it.
The document FR99/10108 presents similar rims adapted to receive lightened supports for the tire tread. In the mounted state, these supports are separated from the inner wall of the tire bead by an appreciable distance, for example about ten centimeters. In the case of the mounting of tire/support assemblies on such rims, it can be seen that the bead has difficulty in following the movement of the support during the fitting of the support on the adapted rim bearing surface. The first bead may lose contact with the pressing roller in the radially outward sense. In this case, the bead may contact the top of the support and there is a risk of contamination due to the lubricant used to facilitate running at low pressure or zero pressure.
As these rims usually have a circumferential well adjacent to the first rim seat (see FIG. 1), the first bead may position itself into this circumferential well during the fitting of the support on the rim bearing surface. There is then a great deal of difficulty in removing it from this position. If the bead remains positioned between the support and the pressing roller, the magnitude of the movement necessary for fitting the support imposes high flexion on the tire which may damage it. Finally, in each case, the correct fitting of the support may remain in doubt.